1. Field of the Invention
This invention relates to a misfire-detecting system for an internal combustion engine, and more particularly to a misfire-detecting system which is adapted to detect a misfire attributable to the fuel supply system.
2. Prior Art
There are conventionally known various kinds of misfire-detecting systems for internal combustion engines, as proposed, for example, by Japanese Provisional Patent Publication (Kokai) No. 4-81548 by the present assignee, which finally determines that the engine is in a misfiring state when misfires have occurred in the engine at a predetermined rate or more, and then alerts the driver to take an appropriate failsafe action to prevent component parts of the exhaust system, especially a catalytic converter for purifying exhaust gas components, of the engine, from being adversely affected by misfires.
In the above proposed conventional system, however, the predetermined misfiring rate is set on the premise that the catalytic converter is normally functioning. As a result, when the catalytic converter has a deteriorated purifying ability, there is a fear that the engine suffers from degraded exhaust emission characteristics before the engine is determined to be in a misfiring state.
In addition, when the purifying ability of the catalytic converter is further deteriorated, occurrence of misfires accelerates the deterioration of the purifying ability, which may result in a shortened life of the catalytic converter.